| Therefore , Myc SERT was co expressed with the endoplasmic reticulum ( ER ) molecular chaperones calnexin , calreticulin and immunoglobulin heavy chain binding protein ( BiP ) , and the foldase , ERp 57 . ^^^ The expression of functional Myc SERT , as determined by an inhibitor binding assay , was enhanced nearly 3 fold by co expressing calnexin , and to a lesser degree on co expression of calreticulin and BiP . ^^^ A physical interaction between Myc SERT calnexin and Myc SERT calreticulin was demonstrated by co immunoprecipitation . ^^^ SERT is the first member of the neurotransmitter transporter family whose folding has been shown to be assisted by the molecular chaperones calnexin , calreticulin , and BiP . . ^^^ |